Surprisingly, there is no generally accepted definition of a laser "pointer".

In the U.S., the federal FDA/CDRH indicates that pointers are "hand-held lasers that are promoted for pointing out objects or locations" with output power less than 5 milliwatts. Promotion of lasers above 5 milliwatts "for pointing and amusement" violates FDA requirements and U.S. law.

(Some may consider this to be a loophole. If a hand-held laser is not promoted for pointing or amusement purposes, then it can be sold.)

In New South Wales (Australia), a pointer is a Schedule 1 Prohibited Weapon: "A laser pointer, or any other similar article, consists of a hand-held, battery-operated device with a power output of more than 1 milliwatt, designed or adapted to emit a laser beam and that may be used for the purposes of aiming, targeting or pointing."

If one wants to own a laser with greater power, it is easy enough to do so. There is the inconvenience of having to run off of mains (AC) power, but then again AC outlets are everywhere, including automobiles (using a $20 inverter).

Also, if an evil person wanted to do harm with a laser beam, it would be easy for them to use a regular laser. A laser pointer restriction would have no effect on them.

What is the maximum power needed for laser pointing?

A power of 50 milliwatts is probably the maximum needed power for almost any laser pointing use. For seeing the laser "dot" on a wall or surface, 5 milliwatts of green is fine. The most demanding general-use application is for pointing out stars (not airplanes!!), when it is necessary to see the beam in mid-air. It takes more power to see the beam than the dot. For this use 5-25 mW should be fine, with a maximum of 50 mW for use in a large group with clear air (few particulates) in an urban environment.

If you like to pop balloons, or put the laser through textured glass for a light show, you may want a more powerful laser. But this is no longer a POINTER application.

Is a laser pointer is not safer than a knife or gun? Which is safer, laser pointer or knife?

It is true that a laser pointer's beam causes much less direct damage to humans than a knife or gun. No one has been injured by a laser pointer, except for a very few eye injuries caused by irresponsible users. However, the potential for serious injuries is primarily due to "bright light distractions" and flashblindings. If a pilot or the driver of a vehicle is distracted or temporarily flashblinded, the laser could do much more damage than a knife or gun.